High Pressure Downhole Pump Assembly

ABSTRACT

A downhole bore hole reciprocating pump apparatus and assembly which provides both a high pressure drilling fluid and a low pressure drilling fluid to the preceding drill bit or preceding downhole equipment or only a high pressure drilling fluid to the preceding drill bit or preceding downhole equipment for an expedient and more efficient removal of the material or rock formation being drilled while providing sufficient fluid volume to remove cuttings from the bore hole and cooling and lubricating of the downhole equipment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application Ser. No. 61/850,910 filed Feb. 26, 2013 by Alan L. Nackerud, which is incorporated by reference herein.

BACKGROUND AND FIELD OF INVENTION

Most conventional well bores are drilled and/or worked over with fluid circulated into the well bore by pumps which are located at the surface. The fluid pressures, volumes and rates delivered to the downhole drill bit and other downhole equipment is limited by the size and capacity of said surface pumps. At times it is advantageous to deliver a higher downhole fluid pressure or deliver both a high and low pressure fluid to enhance drilling and or completion work of a well bore. The present invention employs a new and novel apparatus and method to increase said downhole fluid pressure and deliver both a high pressure fluid and low pressure fluid as described and shown herein with minimal equipment and cost.

SUMMARY OF THE INVENTION

The above and other advantages and features of the present invention will become more readily appreciated and understood from a consideration of the following detailed description taken together with the accompanying drawings in which:

DRAWINGS Figures

FIG. 1 is a cross section side view of a bottom hole assembly with a top flare sub, high pressure downhole pump, high/low pressure sub and drill bit;

FIG. 2 is a cross section top view across the top of the high/low pressure sub;

FIG. 3 is a cross section top view of the high pressure downhole pump across the upper low pressure lateral bores;

FIG. 4 is a cross section top view of the high pressure downhole pump across the upper low pressure inlet points to the large piston bore;

FIG. 5 is a cross section top view of the high pressure downhole pump across the middle of the high pressure downhole pump with the large piston in a center position;

FIG. 6 is a cross section top view of the high pressure downhole pump across the lower low pressure inlet points to the large piston bore;

FIG. 7 is a cross section top view of the high pressure downhole pump across the lower low pressure lateral bores;

FIG. 8 is a cross section side view rotated 22.5 degrees clockwise of the top flare sub, high pressure downhole pump, high/low pressure sub and drill bit;

FIG. 9 is a cross section top view rotated 22.5 degrees clockwise across the top of the high/low pressure sub;

FIG. 10 is a cross section top view rotated 22.5 degrees clockwise of the high pressure downhole pump across the upper high pressure lateral bores;

FIG. 11 is a cross section top view rotated 22.5 degrees clockwise of the high pressure pump across the upper low pressure inlet points to the large piston bore;

FIG. 12 is a cross section top view rotated 22.5 degrees clockwise of the high pressure pump across the middle of the high pressure pump with the large piston in a center position;

FIG. 13 is a cross section top view rotated 22.5 degrees clockwise of the high pressure pump at the lower low pressure inlet points to the large piston;

FIG. 14 is a cross section top view rotated 22.5 degrees clockwise of the high pressure downhole pump across the lower high pressure lateral bores;

FIG. 15 is a cross section side view of the top flare sub, high pressure downhole pump, high/low pressure sub and drill bit with the large piston in the lower position;

FIG. 16 is a cross section side view rotated 22.5 degrees clockwise of the top flare sub, high pressure downhole pump, high/low pressure sub and drill bit with the large piston in the lower position;

FIG. 17 is a cross section side view of the top flare sub, high pressure downhole pump, high/low pressure sub and drill bit with the large piston in the upper position;

FIG. 18 is a cross section side view rotated 22.5 degrees clockwise of the top flare sub, high pressure downhole pump, high/low pressure sub and drill bit with the large piston in the upper position;

FIG. 19 is an enlarged top view of the rod valve;

FIG. 20 is a side view of the rod valve;

FIG. 21 is an enlarged top view of the high pressure downhole pump small piston;

FIG. 22 is a side view of the high pressure downhole pump large piston and small pistons.

REFERENCE NUMERALS

-   1. flare sub -   2. box connection -   3. sub center low pressure bore -   4. flared bore -   5. large set screw plug -   6. alignment pin -   7. weld -   8. split disc check valve -   9. small set screw plug -   10. low pressure fluid bore -   11. small piston bore -   12. high pressure fluid bore -   13. small piston -   14. pump -   15. rod valve end compression spring -   16. rod valve -   17. rod valve end block -   18. rod valve shock compression spring -   19. large piston -   20. large piston bore -   21. high/low pressure sub -   22. low pressure lateral fluid bore -   23. high pressure lateral fluid bore -   24. high pressure sub bore -   25. low pressure slot to center bore -   26. drill bit -   27. low pressure inlet bore -   28. rod valve bore -   29. rod valve end bore

DETAILED DESCRIPTION

Referring to the drawings, there is illustrated in FIGS. 1 through 22 one form of the present invention being a high pressure downhole pump and bottom hole assembly. The present invention works in a well bore with a drill string having a downhole assembly with a top flare sub 1, high pressure downhole pump 14, bottom high/low pressure sub 21 and leading or preceding drill bit 26 or other preceding equipment.

Prior to the upper pump section and lower pump section being attached to each other, rod valves 16 are inserted through the rod valve bores 28 in the large piston 19. Said rod valve bores 28 are of a large enough diameter to allow the free movement of the rod valves 16 within the large piston 19 without excessive drag so that the rod valve end blocks 17 do not prematurely cover the low pressure inlet bores 27. The rod valve shock compression springs 18 are then placed onto the rod valves 16 and then the rod valve end blocks 17 are welded or threadedly attached to the end of the rod valves 16. The rod valve end blocks 17 have small bores through their length to allow some fluid movement above and below so said rod valve end blocks 17 are able to move up and down when activated. The small pistons 13 are then screwed into, welded or otherwise attached to the large piston 19. Said small pistons 13 have a center bore through their length with intersecting lateral bores to allow fluid flow in and out of the large piston bore 20. Each small piston 13 has a split disc check valve 8 or other type valve at its distal end to the large piston 19 connection to allow fluid flow out the distal end of said small piston 13 but not in a reverse direction toward the large piston 19. The rod valves 16, and large piston 19, and small pistons 13 are then aligned and placed inside the large piston bore 20 and the rod valve end bores 29 of the upper pump section and lower pump section. The high pressure downhole pump 14 upper and lower sections are then connected to each other by weld 7, threads or otherwise attached as shown in FIG. 1. The top flare sub 1 is then attached by weld 7, threads, or otherwise attached to the top of the high pressure downhole pump 14. The drill string is then connected by threads or otherwise attached to the top flare sub 1.

The pump 14 body has multiple low pressure fluid bores 10 which run the length of the pump 14. Said low pressure fluid bores 10 are radially located around the outside edge of the diameter of the pump 14. The pump 14 also has multiple high pressure fluid bores 12 which run the length of the pump 14. Said high pressure fluid bores 12 are also radially located near the outside diameter of the pump 14 but offset to the low pressure fluid bores 10. Each said high pressure fluid bore 12 has a split disc check valve 8 or other type valve located at both the top and bottom of said bore which allows fluid to enter at the top of the pump 14 and exit at the bottom of the pump 14 but which does not allow fluid to reverse direction.

As fluid is pumped down the drill string by surface pumps it enters the flare sub 1 and then proceeds into the low pressure fluid bores 10 and down the pump 14 whereby some fluid is allowed to enter multiple low pressure lateral bores 22 and multiple low pressure inlet bores 27 whereby fluid can enter the upper small piston bore 11 and the upper large piston bore 20 and thereby drive or move the large piston 19 and advancing small piston 13. Fluid diversion into the low pressure lateral bores 22 and low pressure inlet bores 27 can be assisted by the depth at which the small set screw plugs 9 and large set screw plugs 5 are screwed into the pump 14 body. The diameter of the large piston 19 is larger than the diameter of the small pistons 13 and thereby when moved creates a higher fluid pressure at the advancing end of the advancing small piston 13. With each reciprocating stroke, high pressure fluid is discharged out the distal end of the advancing small piston bore 11 and into the high pressure lateral bores 23 near the advancing end of the small piston 13 and on to the preceding drill bit 26 or preceding equipment. When the large piston 19 and advancing small piston 13 reaches the end of its stroke the large piston 19 moves the relative rod valve end blocks 17 into a position which uncovers the low pressure inlet bores 27 near the advanced end of the advanced small piston 13 whereby fluid can now enter that portion of the large piston bore 20 while simultaneously the other end of the rod valve end blocks 17 have moved to a position which covers the low pressure inlet bores 27 at the opposing end of the pump 14 whereby fluid is stopped from entering that portion of the large piston bore 20. The pump 14 has effectively reversed direction or reciprocated and with a reverse direction stroke of the large piston 19 causes the same discharge of high pressure fluid at the opposite end of the pump 14 but into the same high pressure fluid bores 12 whereby high pressure fluid then proceeds to the preceding drill bit or preceding equipment.

At the end of each stroke of the large piston 19, both the rod valve shock compression springs 18 and the rod valve end compression springs 15 allow the pump 14 to reciprocate with a minimum of hammering of the large piston 19 and rod valve end blocks 17 yet assist in keeping them in proper position to cover or uncover the low pressure inlet bores 27. Throughout the pump the low pressure lateral bores 22 and the high pressure lateral bores 23 have split disc check valves 8 or other type valves to allow fluid flow in only one desired direction. Throughout the pump 14 the low pressure fluid and high pressure fluid remain separated by virtue of the separate low pressure fluid bores 10 and the high pressure fluid bores 12. When the upper pump section and lower pump section are connected to each other they are aligned to each other by alignment pins 6. Similar alignment pins 6 keep the low pressure fluid bores 10 and high pressure fluid bores 12 aligned at the connection between the pump 14 and high/low pressure sub 21 at the lower end of the pump. The high/low pressure sub 21 allows the low pressure fluid to aggregate or combine back into one sub center low pressure bore 3 while the high pressure fluid remains in multiple separate high pressure sub bores 24. The said multiple separate high pressure sub bores 24 angle inward into matching aligned bores in a drill bit or other downhole completion tool. The pump 14 allows for a high pressure fluid to be used for drilling, completion or other downhole tools but the pump 14 also allows for delivery of a low pressure fluid to ensure that an adequate amount of fluid is delivered for cuttings removals, drill fluid circulation throughout the hole, cooling of tools and other normal purposes for circulating drilling fluid.

It is therefore to be understood that even though numerous characteristics and advantages of the present embodiment have been set forth in the foregoing description, together with the details of the structure and function of the embodiment, the disclosure is illustrative only, and changes may be made within the principles of the embodiment to the full extent indicated by the broad general meaning of the terms in which the claims are expressed and reasonable equivalents thereof and various forms of the present invention can be applied to numerous drilling and completion tools of well bores. 

I claim:
 1. A downhole reciprocating pump apparatus and assembly to increase the pressure of all or a portion of the drilling fluid delivered to the leading drill bit or downhole equipment comprising: (a) a pump with a large piston bore which runs through the center of and longitudinally through the substantial length of said pump wherein a large piston is located and able to reciprocate through said large piston bore, and (b) wherein threadedly, welded or otherwise attached to the top and bottom of said large piston are opposing long small diameter pistons which are positioned inside long small diameter piston bores that extend from the end of the large piston bore to an end point near the pump body distal ends, and (c) wherein numerous small diameter low pressure fluid bores are located outside the perimeter of said large piston bore and run the longitudinal length of said pump which allows low pressure fluid to enter the said long small piston bores and large piston bore and allows a portion of the low pressure fluid to advance to the leading drill bit or preceding other downhole equipment, and (d) wherein numerous small diameter high pressure fluid bores are located axially outside the perimeter of said large piston bore and in an alternating position to said longitudinal low pressure fluid bores and run the longitudinal length of said pump which said high pressure fluid bores are plugged at their top end to only allow high pressure fluid to advance to the leading drill bit or preceding other downhole equipment and not into the upper drill string, and (e) wherein numerous low pressure lateral bores are located near the top and bottom of said pump which intersect said longitudinal low pressure fluid bores and long small diameter piston bores which allows low pressure drilling fluid to enter said long small diameter piston bores, and (f) wherein the low pressure lateral bores are valves which allow drilling fluid flow in only one direction into said long small diameter piston bores, and (g) wherein numerous high pressure lateral bores are located near the top and bottom of the pump which intersect said longitudinal high pressure fluid bores and long small diameter piston bores and allow high pressure fluid to be discharged from said small piston bores into said longitudinal high pressure fluid bores, and (h) wherein the high pressure lateral bores are valves which allow drilling fluid flow in only one direction into said longitudinal high pressure fluid bores, and (i) wherein the large piston has one or more rod valve bores located near the outside edge of said large piston and which extend the length of said large piston wherein long rod valves of a cylindrical shape are inserted and although nearly the same diameter of said rod valve bores are slightly undersized to allow free movement through said rod valve bores, and (j) wherein at the distal ends of said rod valves are an integral or threadedly, welded or otherwise attached rod valve end blocks of a cylindrical shape which mate with similarly positioned bore holes in the pump body at each end of the large piston bore, and (k) wherein lateral low pressure inlet bores are located beyond the distal ends of the large piston bore which radially intersect the rod valve end block bores to the longitudinal low pressure fluid bores which allow drilling fluid to enter the large piston bore when the said rod valve end blocks are in an open position wherein when the large piston moves in one direction of its reciprocation one of the long small pistons retreats from its long small piston bore and the rod valve end blocks located at that end of the pump are in an open position to allow fluid entry into that end of the large piston bore while simultaneously at the opposite end, the rod valve end blocks are in a closed position which stops fluid entry into that end of the large piston bore until the large piston travels its full distance whereupon the rod valve end blocks are pushed into an alternate position whereby the fluid then enters the opposite end of the large piston bore and the large piston reverses direction and reciprocates, and (l). wherein when all interior parts to said pump are placed in the pump the top section of the pump and the bottom section of the pump longitudinal low pressure fluid bores and longitudinal high pressure fluid bores are aligned and alignment pins are placed in alignment pin holes located at the bottom of the top section of the pump and the top of the bottom section of the pump whereupon the two portions of the pump can be welded together or otherwise attached to each other, and
 2. In an apparatus according to claim 1 wherein a top flare sub is threadedly or otherwise attached to a drill string wherein its center bore for drilling fluid is widened or flared to a larger diameter at its bottom to allow for more area of fluid delivery to the pump attached below.
 3. In an apparatus according to claim 2 wherein said top flare sub has alignment pins placed in alignment pin holes located at the bottom of said top flare sub and the top of the top section of the pump whereas said top flare sub and top section of the pump can be welded together or otherwise attached to each other.
 4. In an apparatus according to claim 1 wherein a bottom high/low pressure sub is attached to the bottom of the pump wherein said sub has one or more perimeter high pressure bores at its top that angle toward and align into similar perimeter high pressure bores in the preceding bit or other downhole equipment and wherein said bottom high/low pressure sub has at its bottom one or more axially located perimeter low pressure slots that angle into a center bore which align with a low pressure bore in the center of a preceding bit or other downhole equipment.
 5. In an apparatus according to claim 4 wherein the bottom high/low pressure sub has alignment pins placed in alignment pin holes located at the top of said bottom high/low pressure sub and the bottom of the bottom section of the pump whereas the bottom high/low pressure sub and bottom section of the pump can be welded together or otherwise attached to each other.
 6. In an apparatus according to claim 1 wherein the valves located in the low pressure lateral bores and high pressure lateral bores are split disc check valves which have two independent half circle plate doors rotatable on a hinge pin which allows said doors to swing open when pressure is applied in one direction and allow fluid flow while if no fluid pressure or if fluid pressure is applied from the reverse direction said doors close and abut against the valve body with the assistance of a torsion spring on said hinge pin whereby the fluid cannot reverse direction.
 7. In an apparatus according to claim 1 wherein said long small diameter pistons are hollow with an interior bore and perforated and have a valve located at their distal ends which said valves are closed when advancing and open when retreating which allows low pressure fluid to enter the small diameter pistons interior bore and the small diameter piston bore in the pump body when said small diameter pistons are retreating and alternately when advancing allow high pressure fluid to be discharged.
 8. In an apparatus according to claim 7 wherein the valves are split disc check valves which have two independent half circle plate doors rotatable on a hinge pin which allows said doors to swing open when pressure is applied in one direction and allow fluid flow while if no fluid pressure or if fluid pressure is applied from the reverse direction said doors close and abut against the valve body with the assistance of a torsion spring on said hinge pin whereby the fluid cannot reverse direction.
 9. In an apparatus according to claim 1 wherein rod valve shock compression springs are located on the rod valves between the rod valve end blocks and the large piston and moveable whereupon at the end of the large piston stroke the large piston pushes said rod valve shock compression springs and thereby the said rod valve end blocks into an open position which allows fluid to then enter that end of the large piston bore by way of intersection with said lateral low pressure inlet bores whereby the said rod valve shock compression springs absorb shock and minimize hammering of the rod valves and assist in the reversal of direction of the large piston and long small diameter pistons.
 10. In an apparatus according to claim 1 wherein at the distal ends of the said rod valve end block bores in the pump body where the rod valve end blocks reside are rod valve end compression springs which absorb shock and minimize hammering of the rod valves from the end strokes of the reciprocation of said large piston, said rod valves and said rod valve end blocks and also assist in the reversal of direction of the said large piston, said rod valves and said rod valve end blocks.
 11. In an apparatus according to claim 1 wherein said rod valve end blocks have one or more small bores through their length to allow some fluid to travel from one side of said rod valve end block to the other to allow trapped fluid between the end of the block and the end of the rod valve end block bore to move freely.
 12. In an apparatus according to claim 1 wherein set screws in the exterior wall of the pump body where the lateral low pressure inlet bores are located can be adjusted or screwed in or out to divert or assist in the direction of fluid from the longitudinal low pressure fluid bores into the large piston bore.
 13. A downhole reciprocating pump apparatus and assembly to increase the pressure of all of the drilling fluid delivered to the leading drill bit or downhole equipment comprising: (a) a pump with a large piston bore which runs through the center of and longitudinally through the substantial length of said pump wherein a large piston is located and able to reciprocate through said large piston bore, and (b) wherein threadedly, welded or otherwise attached to the top and bottom of said large piston are opposing long small diameter pistons which are positioned inside long small diameter piston bores that extend from the end of the large piston bore to an end point near the pump body distal ends, and (c) wherein numerous small diameter low pressure fluid bores are located outside the perimeter of said large piston bore and run the longitudinal length of said pump which allows low pressure fluid to enter the said long small piston bores and large piston bore, which said low pressure fluid bores are plugged at their bottom end to not allow low pressure fluid to advance to the leading drill bit or preceding other downhole equipment, and (d) wherein numerous small diameter high pressure fluid bores are located axially outside the perimeter of said large piston bore and in an alternating position to said longitudinal low pressure fluid bores and run the longitudinal length of said pump which said high pressure fluid bores are plugged at their top end to only allow high pressure fluid to advance to the leading drill bit or preceding other downhole equipment and not into the upper drill string, and (e) wherein numerous low pressure lateral bores are located near the top and bottom of said pump which intersect said longitudinal low pressure fluid bores and long small diameter piston bores which allows low pressure drilling fluid to enter said long small diameter piston bores, and (f) wherein the low pressure lateral bores are valves which allow drilling fluid flow in only one direction into said long small diameter piston bores, and (g) wherein numerous high pressure lateral bores are located near the top and bottom of the pump which intersect said longitudinal high pressure fluid bores and long small diameter piston bores and allow high pressure fluid to be discharged from said small piston bores into said longitudinal high pressure fluid bores, and (h) wherein the high pressure lateral bores are valves which allow drilling fluid flow in only one direction into said longitudinal high pressure fluid bores, and (i) wherein the large piston has one or more rod valve bores located near the outside edge of said large piston and which extend the length of said large piston wherein long rod valves of a cylindrical shape are inserted and although nearly the same diameter of said rod valve bores are slightly undersized to allow free movement through said rod valve bores, and (j) wherein at the distal ends of said rod valves are an integral or threadedly, welded or otherwise attached rod valve end blocks of a cylindrical shape which mate with similarly positioned bore holes in the pump body at each end of the large piston bore, and (k) wherein lateral low pressure inlet bores are located beyond the distal ends of the large piston bore which radially intersect the rod valve end block bores to the longitudinal low pressure fluid bores which allow drilling fluid to enter the large piston bore when the said rod valve end blocks are in an open position wherein when the large piston moves in one direction of its reciprocation one of the long small pistons retreats from its long small piston bore and the rod valve end blocks located at that end of the pump are in an open position to allow fluid entry into that end of the large piston bore while simultaneously at the opposite end, the rod valve end blocks are in a closed position which stops fluid entry into that end of the large piston bore until the large piston travels its full distance whereupon the rod valve end blocks are pushed into an alternate position whereby the fluid then enters the opposite end of the large piston bore and the large piston reverses direction and reciprocates, and (l). wherein when all interior parts to said pump are placed in the pump the top section of the pump and the bottom section of the pump longitudinal low pressure fluid bores and longitudinal high pressure fluid bores are aligned and alignment pins are placed in alignment pin holes located at the bottom of the top section of the pump and the top of the bottom section of the pump whereupon the two portions of the pump can be welded together or otherwise attached to each other, and
 14. In an apparatus according to claim 13 wherein a top flare sub is threadedly or otherwise attached to a drill string wherein its center bore for drilling fluid is widened or flared to a larger diameter at its bottom to allow for more area of fluid delivery to the pump attached below.
 15. In an apparatus according to claim 14 wherein said top flare sub has alignment pins placed in alignment pin holes located at the bottom of said top flare sub and the top of the top section of the pump whereas said top flare sub and top section of the pump can be welded together or otherwise attached to each other.
 16. In an apparatus according to claim 13 wherein a bottom high pressure sub is attached to the bottom of the pump wherein said sub has one or more perimeter high pressure bores at its top that angle toward and align into similar perimeter high pressure bores in the preceding bit or other downhole equipment.
 17. In an apparatus according to claim 16 wherein the bottom high pressure sub has alignment pins placed in alignment pin holes located at the top of said bottom high/low pressure sub and the bottom of the bottom section of the pump whereas the bottom high pressure sub and bottom section of the pump can be welded together or otherwise attached to each other.
 18. In an apparatus according to claim 13 wherein the valves located in the low pressure lateral bores and high pressure lateral bores are split disc check valves which have two independent half circle plate doors rotatable on a hinge pin which allows said doors to swing open when pressure is applied in one direction and allow fluid flow while if no fluid pressure or if fluid pressure is applied from the reverse direction said doors close and abut against the valve body with the assistance of a torsion spring on said hinge pin whereby the fluid cannot reverse direction.
 19. In an apparatus according to claim 13 wherein said long small diameter pistons are hollow with an interior bore and perforated and have a valve located at their distal ends which said valves are closed when advancing and open when retreating which allows low pressure fluid to enter the small diameter pistons interior bore and the small diameter piston bore in the pump body when said small diameter pistons are retreating and alternately when advancing allow high pressure fluid to be discharged.
 20. In an apparatus according to claim 19 wherein the valves are split disc check valves which have two independent half circle plate doors rotatable on a hinge pin which allows said doors to swing open when pressure is applied in one direction and allow fluid flow while if no fluid pressure or if fluid pressure is applied from the reverse direction said doors close and abut against the valve body with the assistance of a torsion spring on said hinge pin whereby the fluid cannot reverse direction.
 21. In an apparatus according to claim 13 wherein rod valve shock compression springs are located on the rod valves between the rod valve end blocks and the large piston and moveable whereupon at the end of the large piston stroke the large piston pushes said rod valve shock compression springs and thereby the said rod valve end blocks into an open position which allows fluid to then enter that end of the large piston bore by way of intersection with said lateral low pressure inlet bores whereby the said rod valve shock compression springs absorb shock and minimize hammering of the rod valves and assist in the reversal of direction of the large piston and long small diameter pistons.
 22. In an apparatus according to claim 13 wherein at the distal ends of the said rod valve end block bores in the pump body where the rod valve end blocks reside are rod valve end compression springs which absorb shock and minimize hammering of the rod valves from the end strokes of the reciprocation of said large piston, said rod valves and said rod valve end blocks and also assist in the reversal of direction of the said large piston, said rod valves and said rod valve end blocks.
 23. In an apparatus according to claim 13 wherein said rod valve end blocks have one or more small bores through their length to allow some fluid to travel from one side of said rod valve end block to the other to allow trapped fluid between the end of the block and the end of the rod valve end block bore to move freely.
 24. In an apparatus according to claim 13 wherein set screws in the exterior wall of the pump body where the lateral low pressure inlet bores are located can be adjusted or screwed in or out to divert or assist in the direction of fluid from the longitudinal low pressure fluid bores into the large piston bore. 